1. Field of the Invention
The present invention relates to an inkjet printing apparatus that carries out printing by ejecting ink, and more particularly, to an inkjet printing apparatus that is capable of calculating ink consumption and a method for calculating ink consumption.
2. Description of the Related Art
For estimating the residual amount of ink in an ink tank, it has been known to calculate ink consumption by a dot counting method (see Japanese Patent Laid-Open No. 2005-53110 and Japanese Patent Laid-Open No. 6-126981). This dot counting method is a method for calculating a consumed ink amount by predetermining an amount of ink per one time of ejecting (1 dot) and checking how many times ejecting has been performed, and multiplying this number of times of ejecting by the abovementioned predetermined amount.
Meanwhile, for the purpose of maintaining printing by a printing head in a satisfactory state, a process to recover an ejecting state of the printing head by suction has been generally performed. The ink in an ink tank is consumed also by this recovery process. Conventionally, in this recovery process as well, employed is a method for recognizing ink consumption, in the same manner as the dot counting method, by predetermining a fixed ink amount to be consumed by one time of recovery operation and checking by a printing apparatus the number of times the recovery process has been performed. For example, in Japanese Patent Laid-Open No. 59-194853 (Japanese Patent No. 1814569), it has been disclosed to calculate a total consumption of ink consumed in a printing apparatus by summation of the consumption of ink consumed by a recovery operation and the consumption of ink consumed by an ejecting operation as described above. Also, in the following, not only the method for recognizing an ink consumption by an ejecting operation but also this method for recognizing an ink consumption by a sucking operation are called a “dot counting method.”
However, in the conventional residual ink amount detection by a dot counting method, since an ink consumption corresponding to one time of ejecting or one time of sucking operation has been fixed regardless of individual differences in devices, a relatively large error has sometimes occurred in an ink consumption finally calculated. That is, a relatively large difference occurs between an ink consumption calculated by an operation and an actual ink consumption. When such a difference occurs, the apparatus judges that the residual ink amount has become “0” or a predetermined amount or less although sufficient ink actually remains.
Therefore, the present inventors have keenly examined the causes for an error in the ink consumption calculated as mentioned above. First, as the main cause of a fluctuation in the ink consumption, a fluctuation in the ejecting amount due to individual differences in printing heads, a fluctuation in the suction amount due to individual differences in suction unit (suction pumps), and a fluctuation in the injection amount of ink into the ink tank have been considered. And, as a result of a study on the consumption of ink when an ordinary user has actually carried out printing, the following findings on the fluctuation were obtained.
Here, for conducting the study, the consumption is calculated on the premise of a case where an ordinary user normally used a printing apparatus equipped with an ink tank with an ink capacity of 14 g, that is, performed intermittent printing including discontinuing by use of the printing medium. As concrete numerical values, the number of dots printed per one day with one type of ink is 65.7 million dots, the maximum ejection amount in one dot is 4 ng, the minimum ejection amount is 3.5 ng, the number of times of suction performed per one day for a printing recovery is 12 times, the maximum suction amount is 0.56 g, and the minimum suction amount is 0.5 g.
In addition, as a formula for calculation, the following is used:Ink consumption in ink tank=(ejection amount×number of dots used)+(ink consumption at the time of cleaning the printing head×number of times of suction)  (Expression 1)
When the ink consumption is calculated for the abovementioned conditions, it is determined that the ink in the ink tank is used up by performing printing for 27 days.
FIG. 10 is a view showing an amount of ink (remaining ink) actually remaining in the ink tank when the ink consumption was calculated for the abovementioned conditions and the residual amount in the ink tank was consequently recognized as “0” by cause for that error. Concretely, this is a ratio of error factors when printing and a suction recovery were actually performed at a minimum value of the ejecting amount and a minimum value of the suction amount although a calculation of the ink consumption was performed with the ejecting amount set as a maximum value, and the suction amount, as a maximum value, shown by a graph. As can be understood from FIG. 10, in fact, about a half (47)% of the remaining ink corresponding to an error is due to a fluctuation in the suction amount, and reducing this fluctuation in the suction amount is effective in reducing the error in the ink consumption due to an operation. In addition, by taking into consideration a fluctuation in the ejecting amount besides this fluctuation in the suction amount, the ink consumption calculated by an operation can be further approximated to actual ink consumption.